Gerald Fischer - Academia.edu (original) (raw)
Papers by Gerald Fischer
Background: Spectral analysis of repeatedly evoked potentials (EPs) is challenging since recordin... more Background: Spectral analysis of repeatedly evoked potentials (EPs) is challenging since recordings contain a superposition of evoked signals and background activity. We developed a novel approach, N-interval Fourier Transform Analysis (N-FTA), which allows for reliable separation and accurate assessment of evoked and background spectral components. We applied this approach to spectral analysis of median nerve short latency EPs for identifying spectral bands of clinical relevance. Methods: We performed right median nerve stimulation in two volunteers at 2.46 Hz and 3.95 Hz stimulation rate (600 and 1000 repetitions respectively). We applied N-FTA for splitting the periodically repeated evoked components from irregular background activity and investigated spectral components in the low, medium and high frequency (LF-, MF-, HF-) bands. We present a signal processing approach, which allows for accurately extracting diagnostically relevant features (signal morphology, latency and amplit...
2016 Computing in Cardiology Conference (CinC), Sep 14, 2016
Assessment of endocardial activation using filtered catheter-recorded electrograms has become a s... more Assessment of endocardial activation using filtered catheter-recorded electrograms has become a standard clinical technique. This study aims to assess factors affecting the accuracy of this process. The simulation study confirmed the ability of catheterbased signals to assess relative ("early vs. late") timing of ventricular activation. However, absolute errors were high, amounting to 10% of the activation interval. Computer-based investigations provide insight into how relevant parameters (catheter size and angle, filtering) affect accuracy. This may allow for further improvement of catheter-based techniques.
Methods of Information in Medicine, 2007
Summary Objectives: Activation time (AT) imaging from electrocardiographic (ECG) mapping data has... more Summary Objectives: Activation time (AT) imaging from electrocardiographic (ECG) mapping data has been developing for several years. By coupling 4-dimensional volume data (3D + time) the electrical sequence can be computed non-invasively. In this paper an approach for extracting the ventricular and atrial blood masses for structurally normal hearts by using cine-gated shortaxis data obtained via magnetic resonance imaging (MRI) is introduced. Methods: The blood masses are extracted by employing Active Appearance Models (AAMs). The ventricular blood masses are segmented, applying the AAMs after providing apex cordis and base of the heart in the volume data, whereas the more complex geometry of the atria requires a more specific attempt. On account of this the atrium was divided into three divisions of appearance, where the images of the volume data in the related divisions have a maximum affinity. The first division reaches from the base of the heart to initial visibility of the uppe...
Methods of Information in Medicine, 2006
Summary Objectives: This paper presents an efficient approach for extracting myocardial structure... more Summary Objectives: This paper presents an efficient approach for extracting myocardial structures from given atrial and ventricular blood masses to enable non-invasive estimation of electrical excitation in human atria and ventricles. Methods: Based on given segmented atrial and ventricular blood masses, the approach constructs the myocardial structure directly, in the case that the myocardium can be detected in the volume data, or by using mean model information, in the case that the myocardium cannot be seen in the volume data due to image modalities or artefacts. The approach employs mathematical and gray-value morphology operations. Regulated by the spatial visibility of the myocardial structure in the medical image data especially the atrial myocardium needs to be estimated repeatedly using the a-priori knowledge given by the anatomy. Results: The approach was tested using eight patient data sets. The reconstruction process yielded satisfying results with respect to an efficie...
Conference proceedings : ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Annual Conference, 2004
Methods for noninvasive imaging of electric function of the heart might become clinical standard ... more Methods for noninvasive imaging of electric function of the heart might become clinical standard procedure the next years. Thus, the overall procedure has to meet clinical requirements as easy and fast application. In this study we propose a new electrode array which improves the information content in the ECG map, considering clinical constraints such as easy to apply and compatibility with routine leads. A major challenge is the development of an electrode array which yields a high information content even for a large interindividual variation in torso shape. For identifying regions of high information content we introduce the concept of a locally applied virtual electrode array. As a result of our analysis we constructed a new electrode array consisting of two L-shaped regular spaced parts and compared it to the electrode array we use for clinical studies upon activation time imaging. We assume that one side effect caused by the regular shape and spacing of the new array be that ...
2007 Joint Meeting of the 6th International Symposium on Noninvasive Functional Source Imaging of the Brain and Heart and the International Conference on Functional Biomedical Imaging, 2007
... Bernhard Tilg, Bernhard Pfeifer, Robert Modre, Michael Seger, Christoph Hintermüller, Gerald ... more ... Bernhard Tilg, Bernhard Pfeifer, Robert Modre, Michael Seger, Christoph Hintermüller, Gerald Fischer, Friedrich Hanser Institute of Biomedical Engineering, University for Health Sciences, Medical Informatics and Technology / UMIT Bernhard.Tilg@UMIT.at ...
SPIE Proceedings, 2004
We present two approaches for reconstructing a patient"s atrial myocardium from morpholo... more We present two approaches for reconstructing a patient"s atrial myocardium from morphological image data.Both approaches are based on a segmentation of the left and right atrial blood masses which mark the innerborder of the atrial myocardium. The outer border of the atrial ...
Biomedical Signal Processing and Control, 2007
The forward problem of electrocardiography describes the spatio-temporal source-field relationshi... more The forward problem of electrocardiography describes the spatio-temporal source-field relationship generating the body surface potential (BSP) and, thus, the electrocardiogram (ECG). The paper presents a ventricular and atrial model for simulating cardiac de-and repolarization and the P-, QRS-and T-wave. The atria and the ventricles are coupled, so that electroanatomical function can be simulated at ones. Movement and contraction are not taken into account while an individual geometry, fibre architecture and ECG sensor arrangement including the Wilson central terminal (WCT) as common reference were considered. This in silico whole-heart model can be used for detailed investigations of the nature of the ECG for the normal beat, arrhythmias, ischemia and infarction. In addition, this model was used as a reference tool for developing and testing different electrocardiographic inverse approaches.
International Congress Series, 2004
Current Directions in Biomedical Engineering, 2018
An 18 years old male patient was diagnosed with genetically confirmed hereditary spastic parapleg... more An 18 years old male patient was diagnosed with genetically confirmed hereditary spastic paraplegia of type SPG11 - a rare disease of neurodegeneration. During normal clinical routine investigation, he presented with a moderate sinus bradycardia. The function of the cardiovascular system was investigated by recording electrocardiogram, impedance cardiogram and continuous blood pressure non-invasively. Cardiac function appeared normal in all modalities. Baroreflex sensitivity was strongly increased by a factor of 2.8. Results indicate that further to hyperactivity of deep tendon reflexes, also the responsiveness regarding control of heart rhythm by baroreceptors is significantly increased. This finding provides evidence for the impact of a neurological disorder onto the cardiovascular system and its autonomic control.
Lecture Notes in Computer Science, 2006
In this study an approach for testing electrode array schemes with respect to their ability to im... more In this study an approach for testing electrode array schemes with respect to their ability to improve the resolution of methods for activation time imaging is proposed. First local linear dependency maps are computed using a virtual array method. These maps depict the torso surface areas where the body surface potential is most sensitive to changes in the transmembrane potential. The optimal number and position of the electrodes within the sensitive body surface regions was selected by constructing effort gain (EG) plots. Such a plot depicts the relative attainable rank of the leadfield matrix in relation to the increase in number of electrodes required to build the electrode array. From the sensitivity maps it was found that the BSP is most sensitive to changes in TMP on the upper left frontal and dorsal body surface. The EG analysis revealed that the optimal array meeting clinical requirements and improving the resolution of activation time imaging consists of 125 electrodes.
Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 2001
We present source formulations and computational/validation strategies currently in vogue for non... more We present source formulations and computational/validation strategies currently in vogue for non-invasive imaging of cardiac electrophysiology.
Biomedical Engineering / Biomedizinische Technik, 2013
Cryoablation protocols can be assessed using temperature distributions in the ablated region obta... more Cryoablation protocols can be assessed using temperature distributions in the ablated region obtained from numerical simulations. During in-vivo studies of cardiac cryoablation the exact positioning of the used applicator is not always known, leading to possible deviations between experiments and simulations. To assess the effects of alternative tip-applicator positionings on the temperature profile of the tip-applicator finite element models of different alignments (horizontal and vertical) and insertion depths (1.5-4.5 mm for the vertical alignment) were simulated. Only small deviations in the temperature profiles were found between the simulated variants that mainly depend on the tissue contact area. Quasi-stationary temperatures were in a close range with an absolute difference below 4 • C.
Medical Imaging 2005: Visualization, Image-Guided Procedures, and Display, 2005
For a clinical application of the inverse problem of electrocardiography, a flexible and fast gen... more For a clinical application of the inverse problem of electrocardiography, a flexible and fast generation of a patient's volume conductor model is essential. The volume conductor model includes compartments like chest, lungs, ventricles, atria and the associated blood masses. It is a challenging task to create an automatic or semi-automatic segmentation procedure for each compartment. For the extraction of the
Background: Spectral analysis of repeatedly evoked potentials (EPs) is challenging since recordin... more Background: Spectral analysis of repeatedly evoked potentials (EPs) is challenging since recordings contain a superposition of evoked signals and background activity. We developed a novel approach, N-interval Fourier Transform Analysis (N-FTA), which allows for reliable separation and accurate assessment of evoked and background spectral components. We applied this approach to spectral analysis of median nerve short latency EPs for identifying spectral bands of clinical relevance. Methods: We performed right median nerve stimulation in two volunteers at 2.46 Hz and 3.95 Hz stimulation rate (600 and 1000 repetitions respectively). We applied N-FTA for splitting the periodically repeated evoked components from irregular background activity and investigated spectral components in the low, medium and high frequency (LF-, MF-, HF-) bands. We present a signal processing approach, which allows for accurately extracting diagnostically relevant features (signal morphology, latency and amplit...
2016 Computing in Cardiology Conference (CinC), Sep 14, 2016
Assessment of endocardial activation using filtered catheter-recorded electrograms has become a s... more Assessment of endocardial activation using filtered catheter-recorded electrograms has become a standard clinical technique. This study aims to assess factors affecting the accuracy of this process. The simulation study confirmed the ability of catheterbased signals to assess relative ("early vs. late") timing of ventricular activation. However, absolute errors were high, amounting to 10% of the activation interval. Computer-based investigations provide insight into how relevant parameters (catheter size and angle, filtering) affect accuracy. This may allow for further improvement of catheter-based techniques.
Methods of Information in Medicine, 2007
Summary Objectives: Activation time (AT) imaging from electrocardiographic (ECG) mapping data has... more Summary Objectives: Activation time (AT) imaging from electrocardiographic (ECG) mapping data has been developing for several years. By coupling 4-dimensional volume data (3D + time) the electrical sequence can be computed non-invasively. In this paper an approach for extracting the ventricular and atrial blood masses for structurally normal hearts by using cine-gated shortaxis data obtained via magnetic resonance imaging (MRI) is introduced. Methods: The blood masses are extracted by employing Active Appearance Models (AAMs). The ventricular blood masses are segmented, applying the AAMs after providing apex cordis and base of the heart in the volume data, whereas the more complex geometry of the atria requires a more specific attempt. On account of this the atrium was divided into three divisions of appearance, where the images of the volume data in the related divisions have a maximum affinity. The first division reaches from the base of the heart to initial visibility of the uppe...
Methods of Information in Medicine, 2006
Summary Objectives: This paper presents an efficient approach for extracting myocardial structure... more Summary Objectives: This paper presents an efficient approach for extracting myocardial structures from given atrial and ventricular blood masses to enable non-invasive estimation of electrical excitation in human atria and ventricles. Methods: Based on given segmented atrial and ventricular blood masses, the approach constructs the myocardial structure directly, in the case that the myocardium can be detected in the volume data, or by using mean model information, in the case that the myocardium cannot be seen in the volume data due to image modalities or artefacts. The approach employs mathematical and gray-value morphology operations. Regulated by the spatial visibility of the myocardial structure in the medical image data especially the atrial myocardium needs to be estimated repeatedly using the a-priori knowledge given by the anatomy. Results: The approach was tested using eight patient data sets. The reconstruction process yielded satisfying results with respect to an efficie...
Conference proceedings : ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Annual Conference, 2004
Methods for noninvasive imaging of electric function of the heart might become clinical standard ... more Methods for noninvasive imaging of electric function of the heart might become clinical standard procedure the next years. Thus, the overall procedure has to meet clinical requirements as easy and fast application. In this study we propose a new electrode array which improves the information content in the ECG map, considering clinical constraints such as easy to apply and compatibility with routine leads. A major challenge is the development of an electrode array which yields a high information content even for a large interindividual variation in torso shape. For identifying regions of high information content we introduce the concept of a locally applied virtual electrode array. As a result of our analysis we constructed a new electrode array consisting of two L-shaped regular spaced parts and compared it to the electrode array we use for clinical studies upon activation time imaging. We assume that one side effect caused by the regular shape and spacing of the new array be that ...
2007 Joint Meeting of the 6th International Symposium on Noninvasive Functional Source Imaging of the Brain and Heart and the International Conference on Functional Biomedical Imaging, 2007
... Bernhard Tilg, Bernhard Pfeifer, Robert Modre, Michael Seger, Christoph Hintermüller, Gerald ... more ... Bernhard Tilg, Bernhard Pfeifer, Robert Modre, Michael Seger, Christoph Hintermüller, Gerald Fischer, Friedrich Hanser Institute of Biomedical Engineering, University for Health Sciences, Medical Informatics and Technology / UMIT Bernhard.Tilg@UMIT.at ...
SPIE Proceedings, 2004
We present two approaches for reconstructing a patient"s atrial myocardium from morpholo... more We present two approaches for reconstructing a patient"s atrial myocardium from morphological image data.Both approaches are based on a segmentation of the left and right atrial blood masses which mark the innerborder of the atrial myocardium. The outer border of the atrial ...
Biomedical Signal Processing and Control, 2007
The forward problem of electrocardiography describes the spatio-temporal source-field relationshi... more The forward problem of electrocardiography describes the spatio-temporal source-field relationship generating the body surface potential (BSP) and, thus, the electrocardiogram (ECG). The paper presents a ventricular and atrial model for simulating cardiac de-and repolarization and the P-, QRS-and T-wave. The atria and the ventricles are coupled, so that electroanatomical function can be simulated at ones. Movement and contraction are not taken into account while an individual geometry, fibre architecture and ECG sensor arrangement including the Wilson central terminal (WCT) as common reference were considered. This in silico whole-heart model can be used for detailed investigations of the nature of the ECG for the normal beat, arrhythmias, ischemia and infarction. In addition, this model was used as a reference tool for developing and testing different electrocardiographic inverse approaches.
International Congress Series, 2004
Current Directions in Biomedical Engineering, 2018
An 18 years old male patient was diagnosed with genetically confirmed hereditary spastic parapleg... more An 18 years old male patient was diagnosed with genetically confirmed hereditary spastic paraplegia of type SPG11 - a rare disease of neurodegeneration. During normal clinical routine investigation, he presented with a moderate sinus bradycardia. The function of the cardiovascular system was investigated by recording electrocardiogram, impedance cardiogram and continuous blood pressure non-invasively. Cardiac function appeared normal in all modalities. Baroreflex sensitivity was strongly increased by a factor of 2.8. Results indicate that further to hyperactivity of deep tendon reflexes, also the responsiveness regarding control of heart rhythm by baroreceptors is significantly increased. This finding provides evidence for the impact of a neurological disorder onto the cardiovascular system and its autonomic control.
Lecture Notes in Computer Science, 2006
In this study an approach for testing electrode array schemes with respect to their ability to im... more In this study an approach for testing electrode array schemes with respect to their ability to improve the resolution of methods for activation time imaging is proposed. First local linear dependency maps are computed using a virtual array method. These maps depict the torso surface areas where the body surface potential is most sensitive to changes in the transmembrane potential. The optimal number and position of the electrodes within the sensitive body surface regions was selected by constructing effort gain (EG) plots. Such a plot depicts the relative attainable rank of the leadfield matrix in relation to the increase in number of electrodes required to build the electrode array. From the sensitivity maps it was found that the BSP is most sensitive to changes in TMP on the upper left frontal and dorsal body surface. The EG analysis revealed that the optimal array meeting clinical requirements and improving the resolution of activation time imaging consists of 125 electrodes.
Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 2001
We present source formulations and computational/validation strategies currently in vogue for non... more We present source formulations and computational/validation strategies currently in vogue for non-invasive imaging of cardiac electrophysiology.
Biomedical Engineering / Biomedizinische Technik, 2013
Cryoablation protocols can be assessed using temperature distributions in the ablated region obta... more Cryoablation protocols can be assessed using temperature distributions in the ablated region obtained from numerical simulations. During in-vivo studies of cardiac cryoablation the exact positioning of the used applicator is not always known, leading to possible deviations between experiments and simulations. To assess the effects of alternative tip-applicator positionings on the temperature profile of the tip-applicator finite element models of different alignments (horizontal and vertical) and insertion depths (1.5-4.5 mm for the vertical alignment) were simulated. Only small deviations in the temperature profiles were found between the simulated variants that mainly depend on the tissue contact area. Quasi-stationary temperatures were in a close range with an absolute difference below 4 • C.
Medical Imaging 2005: Visualization, Image-Guided Procedures, and Display, 2005
For a clinical application of the inverse problem of electrocardiography, a flexible and fast gen... more For a clinical application of the inverse problem of electrocardiography, a flexible and fast generation of a patient's volume conductor model is essential. The volume conductor model includes compartments like chest, lungs, ventricles, atria and the associated blood masses. It is a challenging task to create an automatic or semi-automatic segmentation procedure for each compartment. For the extraction of the